In U.S. patent application Ser. No. 07/488,546, filed Mar. 5, 1990, now U.S. Pat. No. 5,040,026 issued Aug. 13, 1991, entitled MULTICOLOR IMAGE FORMING APPARATUS, in the names of Jamzadeh et al. there is disclosed a color electrophotographic apparatus which is capable of providing a photofinishing operation. Such apparatus operates to sequentially scan each of the image frames of an original filmstrip (e.g. a 35 mm color negative film strip) and produce, by an electrophotographic printing process, full-color prints on a non-photosensitive print-receiver sheet, such as a sheet of paper having a thermoplastic coating. The electrophotographic process involves the steps of forming a set of different color-separated toner images (e.g., cyan, magenta and yellow toner images) on a reusable photoconductive recording element, one set for each original image frame, and transferring such images in registration to the print receiver sheet.
To facilitate sheet handling in the above apparatus, as well as to enhance the efficiency of the overall print-making process, each print receiver sheet is considerably larger is size than the commonly desired sizes of photographic prints. Thus, it is disclosed that several color prints be formed on each receiver sheet. For example, assuming a receiver sheet having a size (in inches) of 12.times.18, it is disclosed that nine 4.times.6 prints be produced on the receiver sheet in a three-by-three, two-dimensional array. This three-by-three array, sometimes referred to as a "9-up" format, would be a desirable format due to the current popularity of photographic prints of this 4.times.6 inch size. In the event larger prints (e.g. 5.times.7 inch) are desired, four of such prints may be formed on a receiver sheet of this size, in a two-by-two, or "4-up", format. Upon forming multiple images on a receiver sheet, the receiver sheet is cut to provide the smaller format prints or "snapshots".
To produce full color prints by any of the various non-photographic techniques, e.g., by electrophotographic, thermal/dye-sublimation and ink jet techniques, it is necessary to sequentially record a series of color-separated images, viz., cyan, magenta and yellow images, on an image-recording member. These images are either directly recorded, in registration, on the ultimate print-receiving medium, as is the case for thermal and ink-jet recording, or, as indicated above in the case of electrophotographic recording systems, recorded on a reusable recording element from which the images can be transferred, in registration, to the print-receiving medium. In either case, the information required to produce these color-separated images can be provided by scanning a color negative filmstrip, one frame at a time and pixel-by-pixel, with an electronic scanning device, e.g., a color-responsive charge-coupled device (CCD). Such scanning devices provide a set of color-separated signals, each of such signals representing the spectral content of the photographically recorded image at three different wavelength regions, e.g., the red (R), green (G), and blue (B) spectral regions. Alternatively, the color-separated R, G and B signals can be computer-generated or read out from a ROM (e.g., a compact disk).
In conventional photographic photofinishing the print medium takes the form of a strip of photosensitive paper, and multicolor images are printed directly thereon in the same order as they appear on the filmstrip. A strip format is preferred for the photographic print medium since it is much easier to advance an elongated strip through the chemical baths required to develop the latent images formed thereon than it is to advance sheet material through these processing baths. Moreover, since multiple color-separated images can be printed simultaneously and in registration on a photographic emulsion, it is possible to use the output of a film scanner directly to control the exposure source of the printer with little or no need to buffer or store the scanner output.
But in the case of non-photographic photofinishing, where multiple full-color images are to be formed on a single sheet of printing material, there is a need to store relatively vast quantities of color image information before the printing of the first, multiframe, color-separated image frame can begin. For example, before the first color-separated image of a "9-up" format can be formed on the photoconductive recording element of the electrophotographic printer mentioned above, it is necessary to store twenty-seven color-separated images (i.e., nine images times three color separations each).
The conventional approach to satisfying the storage requirements of the above photofinishing system is to provide two discrete framestores, each being capable of storing values representing the different sets of color-separated signals required to produce a desired multiframe print. Such framestores would operate in a so-called "ping-pong" fashion, one framestore receiving information from the input device while the other framestore is providing information to the printer, and vice versa. A drawback of this approach is cost, each megabyte of data storage being relatively costly, and each framestore requiring 40 or more megabytes of storage in order to store sufficient information to produce a "9-up" print of photographic quality.